Link a USB Key to a client

Hi all,

We have a server (NAS) on which are connected 2 USB keys (dongles) for software protection.
On the other hand, we have 2 client servers (VM Windows 2008). Each one uses a specific dongle on the NAS server (1 dongle corresponds to one and ONLY one client, and won't work on the other client).

I checked "Auto use device" and "connected" each key on each VirtualHere client.

Everything is working fine... :)
...except when both clients restart at the same time : the first one to start uses both keys.

Is there a way to force the use of a key on a specific client ?

Thank you !
Jeff